1. Field of the Invention
This invention relates to devices for drilling and boring through subterranean formations. More specifically, this invention relates to polycrystalline diamond compacts (xe2x80x9cPDCsxe2x80x9d), also known as cutting elements or diamond inserts, which are intended to be installed as the cutting element of a drill bit to be used for boring through rock in any application, such as oil, gas, mining, and/or geothermal exploration, requiring drilling through geological formations.
2. Description of Related Art
Polycrystalline diamond compacts (xe2x80x9cPDCsxe2x80x9d) are used with down hole tools, such as drill bits (including percussion bits; rolling cone bits, also referred to as rock bits; and drag bits, also called fixed cutter bits), reamers, stabilizers and tool joints. A number of different configurations, materials and geometries have been previously suggested to enhance the performance and/or working life of the PDC. The current trend in PDC design is toward relatively thick diamond layers. Typically, thick diamond layers bonded to a tungsten carbide substrate suffer from extremely high residual tensile stresses. These stresses arise from the difference in the thermal expansion between the diamond layer and the substrate after sintering at high temperature and high pressure. These stresses tend to increase with increasing diamond layer thickness. This stress contributes to the delamination and fracture of the diamond layer when the compact is used in drilling.
A polycrystalline diamond compact (xe2x80x9cPDCxe2x80x9d), or cutting element, is typically fabricated by placing a cemented tungsten carbide substrate into a refractory metal container (xe2x80x9ccanxe2x80x9d) with a layer of diamond crystal powder placed into the can adjacent to one face of the substrate. The components are then enclosed by additional cans. A number of such can assemblies are loaded into a high-pressure cell made from a low thermal conductivity, extrudable material such as pyrophyllite or talc. The loaded cell is then placed in a high pressure press. The entire assembly is compressed under high pressure and high temperature conditions. This causes the metal binder from the cemented carbide substrate to xe2x80x9csweepxe2x80x9d from the substrate face through the diamond crystals and to act as a reactive phase to promote the sintering of the diamond crystals. The sintering of the diamond grains causes the formation of a polycrystalline diamond structure. As a result, the diamond grains become mutually bonded to form a diamond mass over the substrate face. The metal binder may remain in the diamond layer within the pores of the polycrystalline structure or, alternatively, it may be removed via acid leeching or optionally replaced by another material, forming so-called thermally stable diamond (ATSD≅). Variations of this general process exist and are described in the related art. This detail is provided so the reader may become familiar with the concept of sintering a diamond layer onto a substrate to form a PDC insert. For more information concerning this process, the reader is directed to U.S. Pat. No. 3,745,623, issued to Wentorf Jr. et al., on Jul. 7, 1973.
While thicker diamond layers are often desirable to increase the wear life of the PDC, as described above, such increases in diamond layer thickness often induce internal stresses at the interface between the diamond and the tungsten carbide substrate interface. Previous approaches to minimize these internal stresses include modifying the geometry of the interface to change the pattern of residual stress. However, usually the change in residual stress is relatively minor because a non-planar interface has little effect on the residual stress distribution in a thick diamond layer. The non-planar features are generally so small as to be regarded as nearly planar in relation to the diamond table thickness on a thick diamond cutter.
A number of approaches to the manufacturing process and application of PDCs with thick diamond layers are well established in related art. The applicant includes the following references to related art patents for the reader""s general familiarization with this technology.
U.S. Pat. No. 4,539,018 describes a method for fabricating cutter elements for a drill bit.
U.S. Pat. No. 4,670,025 describes a thermally stable diamond compact, which has an alloy of liquidus above 700xc2x0 C. bonded to a surface thereof.
U.S. Pat. No. 4,690,691 describes a cutting tool comprised of a polycrystalline layer of diamond or cubic boron nitride which has a cutting edge and at least one straight edge wherein one face of the polycrystalline layer is adhered to a substrate of cemented carbide and wherein a straight edge is adhered to one side of a wall of cemented carbide which is integral with the substrate, the thickness of the polycrystalline layer and the height of the wall being substantially equivalent.
U.S. Pat. No. 4,767,050 describes a composite compact having an abrasive particle layer bonded to a support and a substrate bonded to the support by a brazing filler metal having a liquidus substantially above 700xc2x0 C. disposed there between.
U.S. Pat. No. 4,802,895 describes a composite diamond abrasive compact produced from fine diamond particles in the conventional manner except that a thin layer of fine carbide particles is placed between the diamond particles and the cemented carbide support.
U.S. Pat. No. 4,861,350 describes a tool component, which comprises an abrasive compact bonded to a cemented carbide support body. The abrasive compact has two zones which are joined by an interlocking, common boundary.
U.S. Pat. No. 4,941,891 describes a tool component comprising an abrasive compact bonded to a support which itself is bonded through to an elongated cemented carbide pin.
U.S. Pat. No. 4,941,892 describes a tool component, which comprises an abrasive compact bonded to a support which itself is bonded through an alloy to an elongated cemented carbide pin.
U.S. Pat. No. 5,111,895 describes a cutting element for a rotary drill bit comprising a thin superhard table of polycrystalline diamond material defining a front cutting face, bonded to a less hard substrate.
U.S. Pat. No. 5,120,327 describes a composite for cutting in subterranean formations, which comprises a cemented carbide substrate and a diamond layer adhered to a surface of the substrate.
U.S. Pat. No. 5,176,720 describes a method of producing a composite abrasive compact.
U.S. Pat. No. 5,370,717 describes a tool insert, which comprises an abrasive compact layer having a working surface and an opposite surface bonded to a cemented carbide substrate along an interface. At least one cemented carbide projection extends through the compact layer from the compact/substrate interface to the working surface in which it presents a matching surface.
U.S. Pat. No. 5,469,927 describes a preform cutting element, which comprises a thin cutting table of polycrystalline diamond, a substrate of cemented tungsten carbide, and a transition layer between the cutting table and substrate. The interface between the cutting table and the transition layer is configured and non-planar to reduce the risk of spalling and delamination of the cutting table.
U.S. Pat. No. 5,472,376 describes a tool component, which comprises an abrasive compact layer bonded to a cemented carbide substrate along an interface. The abrasive compact layer has a working surface, on a side opposite to the interface that is flat and presents a cutting edge or point around its periphery. A recess, having a side wall and a base both of which are located entirely within the carbide substrate, extends into the substrate from the interface.
U.S. Pat. No. 5,560,754 describes a method of making polycrystalline diamond and cubic boron nitride composite compacts, having reduced abrasive layer stresses, under high temperature and high pressure processing conditions.
U.S. Pat. No. 5,566,779 describes a drag bit formed of an elongate tooth made of tungsten carbide and having an elongate right cylinder construction. The end face is circular at the end of a conic taper. The tapered surface is truncated with two 180xc2x0 spaced flat faces at 15xc2x0 to about 45xc2x0 with respect to the axis of the body. A PDC layer caps the end.
U.S. Pat. No. 5,590,727 describes a tool component comprising an abrasive compact, having a flat working surface, which presents a cutting edge, and an opposite surface bonded to a surface of cemented carbide substrate to define an interface having at least two steps.
U.S. Pat. No. 5,590,728 describes a preform cutting element for a drag-type drill bit that includes a facing table of superhard material having a front face, a peripheral surface, and a rear surface bonded to a substrate, which is less hard than the superhard material. The rear surface of the facing table is integrally formed with a plurality of ribs, which project into the substrate and extend in directions outwardly away from an inner area of the facing table towards the peripheral surface thereof.
U.S. Pat. No. 5,647,449 describes a crowned insert. The end of the insert is crowned with a PDC layer integrally cast and bonded thereto so that the enlargement is fully surrounded by the PDC crown.
U.S. Pat. No. 5,667,028 describes a polycrystalline diamond composite cutter having a single or plurality of secondary PDC cutting surfaces in addition to a primary PDC cutting surface, where at least two of the cutting surfaces are non-abutting, resulting in enhanced cutter efficiency and useful life. The primary PDC cutting surface is a PDC layer on one end face of the cutter. The secondary PDC cutting surfaces are formed by sintering and compacting polycrystalline diamond in grooves formed on the cutter body outer surface. The secondary cutting surfaces can have different shapes such as circles, triangles, rectangles, crosses, finger-like shapes, or rings.
U.S. Pat. No. 5,685,769 describes a tool compact comprising an abrasive compact layer bonded to a cemented carbide substrate along an interface, with a recess provided that extends into the substrate from the interface. The recess has a shape of at least two stripes, which intersect.
U.S. Pat. No. 5,706,906 describes a cutting element for use in drilling subterranean formations.
U.S. Pat. No. 5,711,702 describes a cutting compact having a superhard abrasive layer bonded to a substrate layer, where the configuration of the interface between the abrasive and the substrate layers is a non-planar, or three dimensional to increase the surface area between the layers available for bonding.
U.S. Pat. No. 5,743,346 describes an abrasive cutting element comprised of an abrasive cutting layer and a metal substrate wherein the interface there between has a tangential chamfer the plane of which forms an angle of about 5xc2x0 to about 85xc2x0 with the plane of the surface of the cylindrical part of the metal substrate.
U.S. Pat. No. 5,766,394 describes a method for forming a polycrystalline layer of ultra hard material where the particles of diamond have become rounded instead of angular in a multiple roller process.
Each of the aforementioned patents and elements of related art is hereby incorporated by reference in its entirety for the material disclosed therein.
In drill bits, which are used to bore through subterranean geologic formations, it is desirable to manipulate the harmful stresses created at the superabrasive substrate interface, the superabrasive surface, and/or at the location of cutter contact with the formation. When present such stresses can reduce the working life of the PDC by causing premature failure of the superabrasive layer. It is also desirable to have PDCs with increasingly thick diamond or cBN superabrasive layers. However, such thick diamond or cBN layers exacerbate the problem of residual stresses. In general, the most damaging tensile stress regions are located on the outer diameter of the cutter in the superabrasive diamond layer just above the diamond carbide interface. High tensile stress regions may also be found on the cutting face. These stresses increase with increasing diamond layer thickness. On standard cutters, the relatively thin diamond table will be in compression near the center of the diamond face. This invention provides a geometry that manipulates the residual stresses and provides the increased strength and working life of thick diamond layers, by, in its preferred embodiment, providing a polycrystalline diamond layer that extends across the top and down the side of the PDC. A xe2x80x9choopxe2x80x9d of diamond is created about the perimeter of the cutter, which serves to significantly reduce the harmful residual stresses while producing a cutter having improved working life and cutting performance. Additionally, this xe2x80x9choopxe2x80x9d has been found to counteract the bending stress at the diamond carbide interface. Moreover, the xe2x80x9choopxe2x80x9d induces compressive forces on the top surface and inner diameter of the diamond layer. These compressive forces serve as a barrier to crack propagation, thereby providing a considerable improvement in fracture toughness of the PDC. An additional benefit of the present invention is the creation of two cutting edges as the PDC wears. Typically, thick diamond cutters have large wear flats, which tend to behave as bearing surfaces, requiring excessive weight on the bit for reasonable penetration rates. This invention addresses this issue because, although it behaves as a typical PDC cutter during initial wear, as the wear increases the wear flat becomes comprised of a carbide center portion surrounded by diamond, thereby creating two cutting edges. The second cutting edge slows the rate of wear flat development and reduces the weight requirement on the bit for acceptable bit penetration rates.
Therefore, it is an object of this invention to provide a PDC with an enhanced residual stress distribution.
It is a further object of this invention to provide a PDC with a xe2x80x9choopxe2x80x9d geometry that favorably manipulates the residual stresses associated with the differences in thermal expansion between the diamond and the substrate.
It is a further object of this invention to provide a PDC that provides the increased strength and working life of thick diamond layers without the associated increase in external diamond surface tensile stresses.
It is a further object of this invention to provide a PDC with a xe2x80x9choopxe2x80x9d region that counteracts the bending stresses at the diamond-carbide interface.
It is a further object of this invention to provide a PDC with a xe2x80x9choopxe2x80x9d region that provides compressive forces, which serve as a barrier to crack propagation, on the top surface and the inner diameter of the diamond layer of the cutter.
It is a further object of this invention to provide a PDC with a xe2x80x9choopxe2x80x9d region that exposes a plurality of cutting edges during normal wear of the cutter.
These and other objectives, features and advantages of this invention, which will be readily apparent to those of ordinary skill in the art upon review of the following drawings, specification, and claims, are achieved by the invention as described in this application.